The present invention generally relates to rotary machines such as steam and gas turbines and, more particularly, is concerned with a rotary machine having a seal assembly to control clearance between the shank portion of rotating rotor blades or “buckets” and a radially inner end of a stationary nozzle of the rotary machine.
Steam and gas turbines are used, among other purposes, to power electric generators. Gas turbines are also used, among other purposes, to propel aircraft and ships. A steam turbine has a steam path which typically includes in serial-flow relation, a steam inlet, a turbine, and a steam outlet. A gas turbine has a gas path which typically includes, in serial-flow relation, an air intake or inlet, a compressor, a combustor, a turbine, and a gas outlet or exhaust nozzle. Compressor and turbine sections include at least one circumferential row of rotating buckets. The free ends or tips of the rotating buckets are surrounded by a stator casing. The base or shank portion of the rotating buckets are flanked on upstream and downstream ends by the inner shrouds of stationary blades disposed respectively upstream and downstream of the moving blades.
The efficiency of the turbine depends in part on the radial clearance or gap between the rotor bucket shank portion angel wing tip(s) (seal plate fins), and a sealing structure of the adjacent stationary assembly. If the clearance is too large, excessive valuable cooling air will leak through the gap between the bucket shank and the inner shroud of the stationary blade, decreasing the turbine's efficiency. If the clearance is too small, the angel wing tip(s) will strike the sealing structure of the adjacent stator portions during certain turbine operating conditions.
In this regard, it is known that there are clearance changes during periods of acceleration or deceleration due to changing centrifugal forces on the buckets, due to turbine rotor vibration, and due to relative thermal growth between the rotating rotor and the stationary assembly. During periods of differential centrifugal force, rotor vibration, and thermal growth, the clearance changes can result in severe rubbing of, e.g., the moving bucket tips against the stationary seal structures. Increasing the tip to seal clearance gap reduces the damage due to metal to metal rubbing, but the increase in clearance results in efficiency loss.